The invention can notably apply to the field of continuous reforming where a catalyst which comes in the form of pellets of substantially equal diameter passes through a chain of reactors arranged vertically. At the base of each one of them, they enter a transfer device known in the technique as a lift pot where they are mixed with a fluid under pressure (hydrogen for example) and blown through a tube towards the upper inlet of the next reactor. At the end of this chain, the catalyst pellets are carried by a fluid current towards a regenerator and, once regenerated, they are again displaced along the chain of reactors. Such a continuous reforming process is for example described in patent U.S. Pat. No. 4,172,027.
During these continuous reforming cycles, a degradation of the catalyst along the circuit followed thereby is generally observed (a phenomenon referred to as attrition). Transportation by blowing causes a crumbling, a bursting of the catalyst pellets and the formation of dust depositions on the grates inside the reactors. The circulation of the catalyst particles in the pipes is modified thereby. It is therefore useful to measure the rate of displacement of the particles in order to control the evolution of the process.
Patent application FR-A-2,699,274 describes a device for measuring flows of particles in a pipe, which implements a process for measuring pressure variations. One or several thin tubes or channels open into a pipe in which a flow of particles to be characterized circulates. The section of each tube is of the same order of magnitude as that of the circulating particles. A fluid is injected through each of these tubes at a predetermined rate and the variations in the pressure of the fluid, resulting from the flowing of the particles past the opening of each tube, are measured.
The velocity of the particles is determined for example by performing an autocorrelation of the signal indicating the pressure variations. Two thin channels, both supplied with fluid, can also open into two different points along the pipe, and the velocity and the section of the circulating particles can be determined by crosscorrelation of the signals indicating respectively the pressure variations in each of the tubes.
The previous device gives precise measurements. However, the implementation thereof requires tanks delivering a fluid at a controlled rate. In some cases: unavailable fluid reserve or incompatibility between the fluid available and those circulating in pipes while carrying along the particles, its implementation may present drawbacks.